The present invention relates to an image forming apparatus and more particularly to a sheet conveying device, a drive control device and a duplex copy unit included in an image forming apparatus as well as to a sheet conveying method and a drive control method.
It is a common practice with a sheet conveying device to drive conveying means respectively located at the upstream side and downstream side in a direction of sheet conveyance by use of a single drive means or respective drive means. Assume that the upstream conveying means rotates to convey a sheet at a speed of u1, that the downstream conveying means rotates to convey it at a speed of u2 equal to u1, and that the two conveying means rotating at such a speed are accelerated. Also, assume that the drive means respectively assigned to the upstream and downstream conveying means are controllable independently of each other. Then, when a sheet extends over both of the two conveying means, the two drive means may be accelerated at the same time. Further, assume that a usual conveying speed before acceleration and a conveying speed after acceleration are up and uk, respectively. Then, the sheet can be surely accelerated if u1 is equal to uK and if u2 is equal to uK.
On the other hand, assume that either one of the upstream and downstream drive means is controlled in speed. For example, assume that the upstream conveying means rotates at a constant speed while the downstream conveying speed is accelerated. Then, the downstream drive means is so controlled as to accelerate the downstream conveying means when a sheet extends over both of the upstream and downstream conveying means. At the same time, the upstream drive means and upstream conveying means are connected via a one-way clutch such that the upstream conveying means follows the rotation of the downstream conveying means. As a result, despite that the conveying speed u2 is higher than the conveying speed u1 (u1=up and u2=uK), the difference in conveying speed between the two conveying means can be absorbed, insuring acceleration.
The requisite with a modern copier, printer, facsimile apparatus, plotter or similar image forming apparatus is high productivity or printing efficiency. To meet this requisite, the conveying speed of, e.g., a duplex copy conveying unit, peripheral unit or paper discharge unit is increasing relative to the conveying speed or process speed of an image forming section. Particularly, an image forming apparatus operable in a duplex copy mode is required to reverse a paper sheet or similar sheet carrying an image on one side thereon with a duplex copy conveying device and again feed it to an image forming section. A higher speed conveying speed is therefore essential with this type of apparatus.
Today, in parallel with the digitization of an image forming apparatus, interleaf control is becoming predominant. The Interleaf control is such that while sheets are constantly conveyed along the path of an image forming apparatus, the feed of sheets from a tray and the refeed of sheets from a duplex copy conveying unit are alternately effected. Therefore, an image forming apparatus with the interleaf control capability does not need an intermediate tray for temporarily stacking sheets.
Japanese Patent Laid-Open Publication No. 63-112626 and Japanese Patent No. 2,846,926, for example, each disclose a particular sheet conveying device for an image forming apparatus. The sheet conveying device taught in Laid-Open Publication No. 63-112626 includes a single drive means for rotating a plurality of conveying means arranged in a duplex copy conveying unit. The sheet conveying device reverses a sheet and then accelerates the sheet as far as a registration roller pair. The sheet conveying device proposed in Patent No. 2,846,926 includes drive means each being assigned to upstream conveying means and downstream conveying means. The drive means allow a sheet to be conveyed at a variable speed in accordance with the condition of conveyance. This is directed toward smooth acceleration and deceleration to be effected even during sheet conveyance. When a sheet extends over both of the two conveying means, the device taught in Patent 2,846,926 controls the two drive means to an equal speed.
The problem with the control over the individual conveying means is that a particular variable-speed drive source must be assigned to each drive means. This, coupled with the fact that both of the two drive sources must be variably controlled, complicates a control system and increases the cost.
Assume that only one of the control means respectively assigned to the upstream and downstream conveying means is controlled. Then, because a one-way clutch intervenes only between the upstream drive means and the upstream conveying means, the downstream conveying means accelerated pulls the upstream conveying means via a sheet being conveyed by the downstream conveying means. As a result, the upstream arrangement exerts a load on the conveyance and is likely to cause the sheet to crease or otherwise deform. This is undesirable from the reliable conveyance standpoint.
As for the sheet conveying device taught in the previously mentioned Laid-Open Publication No. 63-112626, assume that the intermediate conveying unit conveys a sheet toward the registration roller pair. Then, a difference in speed exists between the intermediate conveying unit and the body of the apparatus, i.e., between the conveying speed of the image forming section and that of the intermediate conveying unit. Consequently, a new sheet driven into the intermediate conveying unit is apt to crease or jam the path. Therefore, a new sheet cannot be introduced into the intermediate conveying unit during acceleration, so that productivity or printing efficiency is limited.
The problem with the sheet conveying device disclosed in the previously mentioned Patent No. 2,846,926 is that when a sheet extends both of the two conveying means, the drive means assigned to the two conveying means must be controlled at the same time. The device therefore needs a sophisticated control system. Moreover, the device must assign a particular variable-speed drive source to each drive means, resulting in an increase in cost.
In an image forming apparatus not including an intermediate tray, a sheet is sometimes brought to a stop on a path (path stacking) due to, e.g., an interrupt job or the delay of rearrangement of image data. Should the sheet be stopped at a position where the conveying speed is different, a load would act on the sheet at the time of restart and would thereby cause the sheet to crease.
Assume that the upstream and downstream conveying means each gripping a particular sheet are again driven to convey the sheets. Then, the distance between the sheets is the problem in the aspect of the size reduction of the image forming apparatus. If the upstream and downstream conveying means each are driven by particular drive means, then the drive timing of the upstream drive means may be controlled to adjust the distance between the sheets. However, in the case where the driving force of the downstream drive means is transmitted to the upstream conveying means, the above distance cannot be adjusted. It is therefore likely that the sheet positioned at the upstream side cannot be sensed. This obstructs accurate, reliable sheet conveyance.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 8-217291 and 11-20993.
It is therefore an object of the present invention to provide a sheet conveying device, a drive control device, a duplex copy conveying unit, a sheet conveying method and a drive control method capable of smoothly transferring a sheet from upstream conveying means to downstream conveying means and smoothly conveying even a sheet, which extends over both of the upstream and downstream conveying means, as well as an image forming apparatus including the same.
It is another object of the present invention to provide a sheet conveying device, a drive control device, a duplex copy conveying unit, a sheet conveying method and a drive control method that are low cost and capable of preventing the productivity of copies (printing efficiency) from being lowered as well as an image forming apparatus including the same.
It is a further object of the present invention to provide a sheet conveying device, a duplex copy conveying unit and a sheet conveying device that are low cost and capable of easily adjusting a distance between consecutive sheets and thereby insuring reliable sheet conveyance as well as an image forming apparatus including the same.
In accordance with the present invention, a sheet conveying device includes an upstream and a downstream rotatable conveying mechanism respectively located on an upstream side and a downstream side on a preselected sheet conveyance path. A first and a second drive source respectively cause the upstream and downstream conveying mechanisms to rotate. The second drive source drives the downstream conveying mechanism at a variable conveying speed. A speed adjusting device causes the conveying speed of the upstream conveying mechanism to reflect the conveying speed of the downstream conveying mechanism that is variable.
Also, in accordance with the present invention, a drive control device controls a first and a second drive source for respectively causing an upstream and a downstream rotatable conveying mechanism, which are respectively located at an upstream side and a downstream side on a preselected sheet conveyance path, to rotate. The drive control device includes a speed adjusting device connecting the upstream and downstream conveying mechanisms for causing the conveying speed the upstream conveying mechanism, which is controlled by the second drive source, to reflect the conveying speed of the downstream conveying mechanism. A controller controls the second drive source such that when the conveying speed of the upstream conveying mechanism and that of the downstream conveying mechanism are to be varied, the downstream conveying mechanism rotates at a higher speed than the upstream conveying mechanism.
Further, in accordance with the present invention, a duplex copy conveying unit includes a reversing section for reversing a sheet, and a path for receiving the sheet conveyed from the reversing section. At least an upstream and a downstream rotatable conveying mechanism are respectively located at an upstream side and a downstream side on the path for conveying the sheet from the path to the outside of the path. A first and a second drive source respectively cause the upstream and downstream conveying mechanisms to rotate. The second drive source drives the downstream conveying mechanism at a variable conveying speed. A speed adjusting device causes the upstream conveying mechanism to reflect the conveying speed of the downstream conveying mechanism, which is variable.
Moreover, in accordance with the present invention, in an image forming apparatus for forming an image on a sheet that is conveyed by a sheet conveying device arranged in the apparatus, the sheet conveying device includes an upstream and a downstream rotatable conveying mechanism respectively located on an upstream side and a downstream side on a preselected sheet conveyance path. A first and a second drive source respectively cause the upstream and downstream conveying mechanisms to rotate. The second drive source drives the downstream conveying mechanism at a variable conveying speed. A speed adjusting device causes the conveying speed of the upstream conveying mechanism to reflect the conveying speed of the downstream conveying mechanism that is variable.
In addition, in accordance with the present invention, in a drive control method for controlling the conveying speed of an upstream rotatable conveying mechanism and the conveying speed of a downstream rotatable conveying mechanism, which are respectively located at an upstream side and a downstream side on a preselected sheet conveyance path, a first and a second drive source respectively cause the upstream and downstream conveying mechanisms to rotate. When a sheet extends over both of the upstream and downstream conveying mechanisms, the first drive source and upstream conveying mechanism are caused to slip on each other while the second drive source rotates the downstream conveying mechanism at a higher speed than the upstream conveying mechanism. The increased rotation speed of the downstream conveying mechanism is transmitted to the upstream conveying mechanism to thereby increase the conveying speed of the upstream conveying mechanism.